The present invention relates generally to identifying broadcast stations to which tuners are tuned. More specifically, the present invention relates to attenuating interference when identifying, from a remote location, the broadcast stations to which tuners are tuned.
The commercial broadcast industry and businesses which advertise through the radio frequency (RF) broadcast media need to know the sizes of audiences which are tuned to particular stations relative to other stations at particular times. This need has been met primarily through the use of verbal or written audience participation surveys. With respect to radio a majority of the listening occurs in automobiles. A problem with written surveys is that listeners cannot practically make a record of their listening tendencies while driving.
In order to make a record of listening tendencies while driving, electronic RF monitoring equipment has been used to remotely identify the stations to which tuners may be tuned. Generally speaking, audiences"" radio tuners use predetermined signals, such as local oscillator signals, that are related to the frequencies of the respective radio stations currently being tuned in. The local oscillator signals are broadcast or otherwise emitted from the tuners as very weak signals that sensitive monitoring equipment can detect. The monitoring equipment identifies the radio stations to which tuners are tuned by detecting these local oscillator signals.
This remote monitoring technique is desirable because it does not require cooperation from an audience, hence reducing or eliminating a host of inaccuracies and costs associated with audience participation surveys. Furthermore, large sample sizes may be monitored at low cost relative to audience participation survey techniques.
Typically, prior art electronic RF monitoring systems call for the local oscillator signals to be well above the level of background electronic noise in the area at which the remote monitoring is to occur. One primary source of background electronic noise, or interference, is from the radio stations themselves because the radio stations broadcast near in frequency to the desired local oscillator signal, and with much higher power.
The background electronic noise may cause local oscillator signals at some frequencies to be more readily detectable than at other frequencies leading to station bias in favor of stations whose related local oscillator signals may have a lower level of background noise. One attempt to compensate for this station bias is to tune the monitoring equipment to the radio station or frequency with the lowest amount of signal to noise ratio in order to equalize the detection of the noisiest local oscillator signal with the detection of the other less noisy oscillator signals. Unfortunately, such a strategy results in the reduced sensitivity of the monitoring equipment and a reduced number of incidences that a radio station is identified, or counted, through the detection of the corresponding local oscillator signal.
In addition, conventional monitoring equipment may fail to identify some radio stations due to a weak local oscillator signal emitted from a particular tuner. As such, this weak local oscillator signal from a particular tuner may not be detectable over the background interference. Local oscillator signals that are weaker at particular tuners, but stronger at other tuners results in a reduced number of incidences that a radio station is identified through the detection of the corresponding local oscillator signal.
Prior art conventional remote monitoring systems have failed to adequately solve the problems associated with interference induced station bias without reducing the sensitivity of the monitoring equipment.
Accordingly, it is an advantage of the present invention that an interference attenuating remote audience survey system and method are provided.
Another advantage is that the present invention improves the accuracy of audience survey data.
It is another advantage that improved accuracy is achieved by improving on the ability of the system to detect audience survey data through the attenuation of interference.
Yet another advantage is that the present invention achieves a compact size through an efficient configuration.
The above and other advantages of the present invention are carried out in one form by an interference attenuating remote audience survey system for identifying radio stations to which tuners are tuned, the tuners having local oscillator (LO) signals emitted therefrom. The system includes a controller configured to select one of the LO signals associated with one of the radio stations. A first antenna senses a first signal in a detection zone of the first antenna, the first signal including the one of the LO signals and an interference signal. A second antenna receives a second signal, the second signal including the interference signal. A shield element is positioned between the second antenna and the detection zone for shielding the second antenna from receiving the one of the LO signals. A combiner is in communication with each of the first and second antennas. The combiner subtractively combines the first and second signals to produce a third signal, the interference signal being attenuated from the third signal. A receiver is in communication with the combiner and the controller. The receiver is configured to detect the selected one of the LO signals within the third signal to determine that one of the tuners is tuned to the one of the radio stations.
The above and other advantages of the present invention are carried out in another form by a method of attenuating interference in a remote audience survey system configured to identify radio stations to which tuners are tuned. The tuners have local oscillator (LO) signals emitted therefrom and the system includes a first antenna and a second antenna. The method calls for sensing a first signal in a detection zone of the first antenna, the first signal including one of the LO signals and an interference signal. The method further calls for receiving a second signal at the second antenna, the second antenna being shielded from receiving the one of the LO signals. A phase shift component is provided to the second signal to substantially cancel a phase difference between the second signal and the interference signal within the first signal. An amplitude component is applied to the second signal to substantially cancel an amplitude difference between the second signal and the interference signal within the first signal. The first and second signals are subtractively combined to produce a third signal, the interference signal being attenuated from the third signal.